Initial Reactions to the District 1 D-STAR Proposal
Written by Jeff Goeke-Smith(KC8PUN) and Dennis Boone(KB8ZQZ)
Portions in Red are alterations made after the 7/10/2007 D-Star meeting
Overview of D-Star
In the late 1990s, the Japan Amateur Radio League obtained funding from the Japanese government to explore digital radio technology and develop a specification for digital voice and data communications in the amateur radio field. This money was sub-granted to outside organizations, primarily Icom, to do the actual development work. The current specification was adopted in about 1999.
D-Star provides both voice and data communications, both of which are carried over the air in digital form. Simultaneous transmission of voice and data is possible, however there are various limitations. Radios may communicate directly with each other, or via a repeater. Repeaters may be interlinked using radio linking hardware, or via the internet. Voice and high speed data are repeated using different hardware. Low speed data travels through the voice repeater network.
Current D-Star operates on the 2m, 70cm, and 23cm amateur radio bands, though nothing about the technology limits which additional bands could be added. (FCC regulations likely prevent using the technology below 50 MHz.) Backbone linking hardware operates on the 10 GHz band.
Low speed data service provides 1200 bit/sec data communication through the D-Star network. This data rate is suitable for shelter operations and the like, and is equivalent to the most commonly used speed on older amateur radio packet (AX.25) networks. It is not suitable for internet access to browse the web or access email.
High speed data service, available only on the 23cm band, provides 128,000 bit/sec (peak; actual could be half that rate) data communication through the D-Star network. This type of access is suitable for web/email internet access. With a fully configured repeater system available, it is possible to access the internet over the air, though the documentation fails to explain how to do so.
A D-Star repeater system includes a controller which manages some aspects of the distribution of voice and data channels among its various components.
Full-featured D-Star systems include a gateway computer which is able to provide various kinds of network services. Custom data services could be implemented on this gateway. In addition, the gateway is responsible for managing links to other repeaters which travel across the internet.
The D-Star specification is nominally open, that is, it is published, and is not encumbered by any patents or copyrights. Any organization is free to implement the specification. At this time, only Icom is selling mass produced hardware. At least one engineer has built a low-power home-brew transceiver which successfully interoperates with the Icom hardware, and he is considering selling kits or assembled radios in small lot quantities through his private engineering firm.
While the D-Star specification is open, it calls for the use of the AMBE voice codec (a defined transformation which converts analog voice signals into digital signals) which is a trade secret. AMBE is a relative of IMBE, which is used in the APCO P25 specification commonly found in digital public safety radios such as the MPSCS system. Both AMBE and IMBE are owned by Digital Voice Systems, Inc. These codecs are available in the form of integrated circuits -- chips -- at a manageable cost, but a license for the software implementation of the codec is priced at $20,000 plus royalties, and probably requires signing a non-disclosure agreement. Thus, the only practical form is the chip.
Reactions to the proposal
The system described by the proposal, at least with our current understanding of the D-STAR technology, does not fulfill the goals which are stated or implied, will be relatively unreliable, and may be infeasible to build as specified.
Tonight, I saw an explicit set of goals. They were, as stated:
1) Create a Digital Radio link between all District 1 EOCs.
2) Provide a backup solution to MPSCS.
First, as described by the proposal, the voice and data repeaters would be interlinked via the Internet. Thus, each repeater site would require an uplink to the internet, which must be at least a very good DSL or Cable Modem connection. This connection must provide, per documentation, 768 kilobits per second of throughput in each direction.
According to KC8VAB, the actual needed bandwidth was much less than this, however, he did not have specific numbers of what was required.
As a voice communication application, data must travel with relatively little delay through the connection. If the connection goes down, that repeater will be disconnected from all other repeaters in this network. We find no recurring funding for the Internet connection in this proposal. If existing internet service is to be used, then appropriate firewall modifications and network addressing will be required. Some IT organizations, such as the City of Lansing's, may well be unwilling to make the needed changes.
All of the above still stands. This proposal does not and will not address these issues.
Second, it is proposed to build new repeaters in both the 2m band and 70cm bands. It is unknown whether the Michigan Area Repeater Council (MARC) has any channels available, but at last check, both bands were closed. One of the touted advantages of D-Star is that it uses half the bandwidth of a traditional analog repeater system. However, even if an existing analog allocation can support two digital repeaters, an open allocation still must be found, and analog systems will continue to exist for the foreseeable future. Thus, the narrower spectrum usage does little to alleviate this problem. We believe that MARC will be unlikely to provide coordination's on these bands, and unlikely to grant spacing or frequency exceptions which might make it possible to squeeze them in.
As stated in a later email by Dennis, we have found that MARC is allocating coordinations on a provisional basis. Although some people believe that these provisional coordinations will become permanent, I see no evidence that we should rely upon that for this proposal. Without repeater pairs, much of this system becomes useless.
Third, the user interface documented in the radio manual is very complicated. Among other issues, communication between counties in the proposed configuration would require that the person operating the radio effectively enter a route through the repeater network from source to destination, listing the call signs of their own station and the called station, as well as those of the repeaters through which they enter and exit the network. Certain arbitrary conventions must be specified at appropriate times. Documentation and training will have to be developed and regularly applied in order to maintain operator familiarity with the system. Aggravating the problem is the fact that while most ARPSC operators own and regularly use more traditional equipment, few individuals are purchasing D-Star hardware. The high cost and limited community of users make this trend likely to continue for the foreseeable future.
As part of this process, there is an intent to create a working group that would also provide training. I am not convinced that even with this group, the problem described above is materially altered.
Fourth, while the system supports simultaneous voice and data operation, there are serious limitations as to how this capability can be used. For example, one cannot transmit data while receiving voice, as receive is disabled while transmitting. Thus, one radio will only be reasonably useful as a digital voice or a digital low speed data station at any one time. In addition, this system will only provide data connections at speeds comparable to existing packet radio stations. It is not feasible to browse the web or access e-mail using e.g. Outlook with a link this slow. We see no indication of the nature of service these low speed data links would connect to. Given the low data rate, one would need some sort of custom server to provide any viable messaging services. Creating such a service appears to be possible, but no such application is available out of the box. The alternative, keyboard to keyboard communications, has proven unproductive in Lansing and Ingham County drills. We question whether this 1200 baud data channel is adequately sized for communications between EOCs.
According to several members, the use of voice and data at the same time is well supported and works seamlessly. I don't understand how based on the documentation. I believe the other above concerns still stand.
Winlink is being suggested as an addition to this system. I am not familiar with winlink enough, or how to interlink it with D-Star, to give a strong opinion as to if it would sufficiently alleviate the problems listed above.
Fifth, we feel a few budget items are under priced. For the EOC installations, the antenna and coax pricing seems low. For the repeater installations, given the current price of metals, $500 for duplexers seems overly optimistic.
As for the duplexer pricing, these are small, low power duplexers, which is why the cost is so low.
Sixth, the repeater systems to be installed in each county do not include budget items for antennas, coax, or lightning suppression. To be worthwhile, these systems will require location on a tower at the 60' level or higher, and the site will need appropriate climate control, redundant power, and high speed internet access. Some sites likely have these things, but it would be surprising if every site had all of them. Some of them can be quite costly.
While budget for the antennas, coax, and lighting protection was added to the proposal, the location, and arrangements for facilities are not covered and not intended to be covered by the grant. Those issues were to be placed on the county level groups to sort out.
Finally, we feel that the expenditure of this much money should achieve something which is urgently needed, and which cannot be accomplished at lesser cost. To that end, we offer an alternative to the proposed solution. While each system has its issues, we believe that equivalent voice communications channels could be accomplished with 80 meter or 40 meter HF radios using near-vertical-incidence skywave antennas at each of the proposed sites, at a cost of about $2000 per site. Some sites, such as Lansing, already have part of this solution in place. With the addition of a PACTOR modem, one could provide comparable data rates to each site, at a total site cost of $3000. This setup would not rely upon repeater sites, nor would it rely on Internet connectivity for communications.
I saw nothing tonight to indicate that the above summary was wrong.
Evaluation of the proposed (or any other) system should include an understanding of the place the system would hold in the redundancy hierarchy. Specifically, should one have three deep redundancy in the proposed system, or is it one part of a larger system? We don't know the answer to this question, but we observe that dependency on the commercial internet for repeater linking squarely places the current proposal outside of the former category.
As per the goal statement, this is a third layer backup to MPSCS.
May 23, 2007
Tom,
Jeff just discovered that under recent Repeater Council rule changes, it may now be possible to get _provisional_ coordinations on the 2m and 70cm bands for D-Star repeaters. These will be granted on splinter frequencies between existing coordinations. However, there are a number of limitations:
1. No protection from interference complaints is afforded; any existing repeaters have priority, and the operator of the D-Star system is required to resolve any issues.
2. Provisional coordinations of this type are granted under the Council's Developmental Operating Guidelines, and are therefore valid for a maximum of three years.
3. Coordinations may be altered at any time by the Council.
4. There are limits on the proximity of a D-Star repeater to existing repeaters of 70 miles on the same channel, or 20 miles on an adjacent channel.
We don't feel this new info changes our analysis. It is not conducive to emergency management operations to have a repeater subject to coordination changes on a whim, and the spacing and interference issues are bound to cause problems.
De
Portions in Red are alterations made after the 7/10/2007 D-Star meeting
Overview of D-Star
In the late 1990s, the Japan Amateur Radio League obtained funding from the Japanese government to explore digital radio technology and develop a specification for digital voice and data communications in the amateur radio field. This money was sub-granted to outside organizations, primarily Icom, to do the actual development work. The current specification was adopted in about 1999.
D-Star provides both voice and data communications, both of which are carried over the air in digital form. Simultaneous transmission of voice and data is possible, however there are various limitations. Radios may communicate directly with each other, or via a repeater. Repeaters may be interlinked using radio linking hardware, or via the internet. Voice and high speed data are repeated using different hardware. Low speed data travels through the voice repeater network.
Current D-Star operates on the 2m, 70cm, and 23cm amateur radio bands, though nothing about the technology limits which additional bands could be added. (FCC regulations likely prevent using the technology below 50 MHz.) Backbone linking hardware operates on the 10 GHz band.
Low speed data service provides 1200 bit/sec data communication through the D-Star network. This data rate is suitable for shelter operations and the like, and is equivalent to the most commonly used speed on older amateur radio packet (AX.25) networks. It is not suitable for internet access to browse the web or access email.
High speed data service, available only on the 23cm band, provides 128,000 bit/sec (peak; actual could be half that rate) data communication through the D-Star network. This type of access is suitable for web/email internet access. With a fully configured repeater system available, it is possible to access the internet over the air, though the documentation fails to explain how to do so.
A D-Star repeater system includes a controller which manages some aspects of the distribution of voice and data channels among its various components.
Full-featured D-Star systems include a gateway computer which is able to provide various kinds of network services. Custom data services could be implemented on this gateway. In addition, the gateway is responsible for managing links to other repeaters which travel across the internet.
The D-Star specification is nominally open, that is, it is published, and is not encumbered by any patents or copyrights. Any organization is free to implement the specification. At this time, only Icom is selling mass produced hardware. At least one engineer has built a low-power home-brew transceiver which successfully interoperates with the Icom hardware, and he is considering selling kits or assembled radios in small lot quantities through his private engineering firm.
While the D-Star specification is open, it calls for the use of the AMBE voice codec (a defined transformation which converts analog voice signals into digital signals) which is a trade secret. AMBE is a relative of IMBE, which is used in the APCO P25 specification commonly found in digital public safety radios such as the MPSCS system. Both AMBE and IMBE are owned by Digital Voice Systems, Inc. These codecs are available in the form of integrated circuits -- chips -- at a manageable cost, but a license for the software implementation of the codec is priced at $20,000 plus royalties, and probably requires signing a non-disclosure agreement. Thus, the only practical form is the chip.
Reactions to the proposal
The system described by the proposal, at least with our current understanding of the D-STAR technology, does not fulfill the goals which are stated or implied, will be relatively unreliable, and may be infeasible to build as specified.
Tonight, I saw an explicit set of goals. They were, as stated:
1) Create a Digital Radio link between all District 1 EOCs.
2) Provide a backup solution to MPSCS.
First, as described by the proposal, the voice and data repeaters would be interlinked via the Internet. Thus, each repeater site would require an uplink to the internet, which must be at least a very good DSL or Cable Modem connection. This connection must provide, per documentation, 768 kilobits per second of throughput in each direction.
According to KC8VAB, the actual needed bandwidth was much less than this, however, he did not have specific numbers of what was required.
As a voice communication application, data must travel with relatively little delay through the connection. If the connection goes down, that repeater will be disconnected from all other repeaters in this network. We find no recurring funding for the Internet connection in this proposal. If existing internet service is to be used, then appropriate firewall modifications and network addressing will be required. Some IT organizations, such as the City of Lansing's, may well be unwilling to make the needed changes.
All of the above still stands. This proposal does not and will not address these issues.
Second, it is proposed to build new repeaters in both the 2m band and 70cm bands. It is unknown whether the Michigan Area Repeater Council (MARC) has any channels available, but at last check, both bands were closed. One of the touted advantages of D-Star is that it uses half the bandwidth of a traditional analog repeater system. However, even if an existing analog allocation can support two digital repeaters, an open allocation still must be found, and analog systems will continue to exist for the foreseeable future. Thus, the narrower spectrum usage does little to alleviate this problem. We believe that MARC will be unlikely to provide coordination's on these bands, and unlikely to grant spacing or frequency exceptions which might make it possible to squeeze them in.
As stated in a later email by Dennis, we have found that MARC is allocating coordinations on a provisional basis. Although some people believe that these provisional coordinations will become permanent, I see no evidence that we should rely upon that for this proposal. Without repeater pairs, much of this system becomes useless.
Third, the user interface documented in the radio manual is very complicated. Among other issues, communication between counties in the proposed configuration would require that the person operating the radio effectively enter a route through the repeater network from source to destination, listing the call signs of their own station and the called station, as well as those of the repeaters through which they enter and exit the network. Certain arbitrary conventions must be specified at appropriate times. Documentation and training will have to be developed and regularly applied in order to maintain operator familiarity with the system. Aggravating the problem is the fact that while most ARPSC operators own and regularly use more traditional equipment, few individuals are purchasing D-Star hardware. The high cost and limited community of users make this trend likely to continue for the foreseeable future.
As part of this process, there is an intent to create a working group that would also provide training. I am not convinced that even with this group, the problem described above is materially altered.
Fourth, while the system supports simultaneous voice and data operation, there are serious limitations as to how this capability can be used. For example, one cannot transmit data while receiving voice, as receive is disabled while transmitting. Thus, one radio will only be reasonably useful as a digital voice or a digital low speed data station at any one time. In addition, this system will only provide data connections at speeds comparable to existing packet radio stations. It is not feasible to browse the web or access e-mail using e.g. Outlook with a link this slow. We see no indication of the nature of service these low speed data links would connect to. Given the low data rate, one would need some sort of custom server to provide any viable messaging services. Creating such a service appears to be possible, but no such application is available out of the box. The alternative, keyboard to keyboard communications, has proven unproductive in Lansing and Ingham County drills. We question whether this 1200 baud data channel is adequately sized for communications between EOCs.
According to several members, the use of voice and data at the same time is well supported and works seamlessly. I don't understand how based on the documentation. I believe the other above concerns still stand.
Winlink is being suggested as an addition to this system. I am not familiar with winlink enough, or how to interlink it with D-Star, to give a strong opinion as to if it would sufficiently alleviate the problems listed above.
Fifth, we feel a few budget items are under priced. For the EOC installations, the antenna and coax pricing seems low. For the repeater installations, given the current price of metals, $500 for duplexers seems overly optimistic.
As for the duplexer pricing, these are small, low power duplexers, which is why the cost is so low.
Sixth, the repeater systems to be installed in each county do not include budget items for antennas, coax, or lightning suppression. To be worthwhile, these systems will require location on a tower at the 60' level or higher, and the site will need appropriate climate control, redundant power, and high speed internet access. Some sites likely have these things, but it would be surprising if every site had all of them. Some of them can be quite costly.
While budget for the antennas, coax, and lighting protection was added to the proposal, the location, and arrangements for facilities are not covered and not intended to be covered by the grant. Those issues were to be placed on the county level groups to sort out.
Finally, we feel that the expenditure of this much money should achieve something which is urgently needed, and which cannot be accomplished at lesser cost. To that end, we offer an alternative to the proposed solution. While each system has its issues, we believe that equivalent voice communications channels could be accomplished with 80 meter or 40 meter HF radios using near-vertical-incidence skywave antennas at each of the proposed sites, at a cost of about $2000 per site. Some sites, such as Lansing, already have part of this solution in place. With the addition of a PACTOR modem, one could provide comparable data rates to each site, at a total site cost of $3000. This setup would not rely upon repeater sites, nor would it rely on Internet connectivity for communications.
I saw nothing tonight to indicate that the above summary was wrong.
Evaluation of the proposed (or any other) system should include an understanding of the place the system would hold in the redundancy hierarchy. Specifically, should one have three deep redundancy in the proposed system, or is it one part of a larger system? We don't know the answer to this question, but we observe that dependency on the commercial internet for repeater linking squarely places the current proposal outside of the former category.
As per the goal statement, this is a third layer backup to MPSCS.
May 23, 2007
Tom,
Jeff just discovered that under recent Repeater Council rule changes, it may now be possible to get _provisional_ coordinations on the 2m and 70cm bands for D-Star repeaters. These will be granted on splinter frequencies between existing coordinations. However, there are a number of limitations:
1. No protection from interference complaints is afforded; any existing repeaters have priority, and the operator of the D-Star system is required to resolve any issues.
2. Provisional coordinations of this type are granted under the Council's Developmental Operating Guidelines, and are therefore valid for a maximum of three years.
3. Coordinations may be altered at any time by the Council.
4. There are limits on the proximity of a D-Star repeater to existing repeaters of 70 miles on the same channel, or 20 miles on an adjacent channel.
We don't feel this new info changes our analysis. It is not conducive to emergency management operations to have a repeater subject to coordination changes on a whim, and the spacing and interference issues are bound to cause problems.
De